In this paper we introduce a dual-input actuator, based on an epicyclic gear train, called parallel force∕velocity actuator (PFVA) designed for variable response manipulation. The focus of this work is to formulate a parametric representation for internal and external power flows, and effective inertia in this actuator. Dimensionless criteria have been developed to judge the design of a PFVA, based on the above phenomena. These criteria are then related to two fundamental dimensionless parameters of a PFVA: (i) a design parameter called the relative scale factor that describes the relative kinematic scaling between the two inputs of the PFVA and (b) an operational parameter called the velocity mixing ratio that represents the velocities of the inputs relative to each other. Some numerical examples have been considered using PFVA designs based on positive-ratio drives to convey the practical implication of our parametric models. Based on this study a set of design and operational guidelines has been suggested, which we believe will be useful to the designer in evaluating PFVA designs and operational scenarios on the basis of power-flow and effective inertias. As a representative result, it was observed that the efficiency of a PFVA decreases approximately 19% from the basic efficiency when the relative scale factor was increased approximately 6.5 times (from 4.7 to 25.27) and the velocity mixing ratio was increased 10 times (from 4.16 to 41.6).